The invention relates to a method for checking the gas tightness of a fuel cell system. Furthermore, the invention relates to an arrangement for checking the gas tightness of a fuel cell system.
A fuel cell system which is operated with hydrogen gas (H2) has one or more hydrogen tanks as well as a fuel cell. Such hydrogen tanks can be embodied, for example, as cylinders for use for a motor vehicle, in which cylinders the hydrogen is stored at a raised pressure of approximately 700 bar. If a plurality of such hydrogen tanks are arranged in the motor vehicle, the range of the motor vehicle can be correspondingly configured.
Since gaseous hydrogen is neutral in terms of smell and reacts exothermally with oxygen from the air over a wide ignition range, even in the case of low ignition energy, hydrogen sensors can be used for a fuel cell system in order to detect escaping hydrogen. Apart from costs, which are caused by the use of such hydrogen sensors, said sensors also have a considerable fault rate. Furthermore, hydrogen sensors age relatively quickly and are generally also sensitive to water vapor. A hydrogen sensor can be used only to monitor that area of the fuel cell system to which the hydrogen sensor is assigned, in which case it is also necessary to bear in mind that there are further areas in which monitoring is not carried out.
Document DE 10 2006 025 125 A1 describes a method for detecting leaking locations in a fuel cell system which comprises a hydrogen storage tank, a main shutoff valve and a secondary shutoff valve in a feed line. When switching off occurs, the main shutoff valve is closed, wherein the fuel cells are temporally left operating. Furthermore, the pressure in the feed line between the valves is measured. If the measured pressure has reached a predetermined switch-off pressure, the secondary shutoff valve is closed. At the next system start, the pressure is measured before the shutoff valves are opened, and the measured pressure is compared with the stored pressure. If a value of the present pressure measurement is lower than a value of the stored pressure measurement, this is an indication that the feed line between the shutoff valves has leaking locations. If the measured pressure is higher than the stored pressure, this is an indication that the primary valve has leaking locations.
A gas leak detecting device for a fuel cell system is known from document DE 11 2005 001 818 T5. The fuel cell system comprises here a fuel cell, a fuel gas feed source, a feed passage for the fuel gas, a discharging passage for discharging the fuel gas from the fuel cell, and an emptying valve, arranged in the discharging passage, for adapting a fuel gas quantity discharged by the fuel cell. The gas leak detecting device has a feed quantity detector, arranged in the feed passage, for detecting a fuel gas feed quantity, wherein the feed passage comprises a first passage which is arranged downstream of the feed quantity detector, wherein the fuel cell comprises a second passage through which the fuel gas flows. The discharging passage comprises a third passage which is arranged upstream of the emptying valve. Furthermore, the gas leak detecting device comprises a consumption quantity calculation device for calculating a fuel gas quantity consumed by the fuel cell, a pressure detector for detecting a pressure of the fuel gas in a leak detecting passage including the three passages, a change quantity calculation device for determining a change in the pressure and for calculating a change in the fuel gas quantity in the gas leak detecting passage owing to the change in the pressure of the fuel gas and a differential quantity calculation device for calculating a difference between the detected quantity of fed-in fuel gas and the total quantity of the consumed fuel gas as well as the change in the fuel gas quantity in the gas leak detecting passage.
A diagnostic method for detecting component faults in a fuel cell anode subsystem is known from document DE 10 2007 060 172 A1. In this context, a fuel flow is estimated by injectors and compared with a model which is based on system parameters. An observer-based model is used to determine a residual value of the difference between the hydrogen supply and the consumed hydrogen, wherein the residual value is compared with a limiting value range.